Formation of Iron Oxides by Surface Oxidation of Iron Plate

Oxidation of iron plates (α-phase) at high temperatures and in atmospheric conditions was monitored.The composition of oxidation products was analyzed with XRD, Raman and Mössbauer spectroscopies, whereas the morphologies of oxidation products were inspected by FE-SEM.The oxidation products formed at 300 and 400 °C consisted dominantly of magnetite and small fractions of hematite, whereas at 500 and 600 °C hematite was the dominant phase, as shown by XRD.In all these samples Raman spectra showed the presence of hematite in the outer oxidation layer.FE-SEM analysis showed the formation of nanowires at 500 °C and vertically grown hematite spikes against the lower oxidation layers at 600 °C.Oxidation products formed at 800 °C consisted of wüstite (Fe 1-x O) as the dominant phase, nonstoichiometric magnetite (Fe 3-x O 4 ) and hematite (α-Fe 2 O 3 ) in small fractions.The surface of these oxidation layers showed a hierarchical microstructure, as well as the hexagonal hematite rods vertically grown against the lower oxidation layers.The formation of the oxidation products can be considered a process which includes the oxidation of α-Fe to Fe 1-x O and its transformation to Fe 3-x O 4 that further transforms to α-Fe 2 O 3 , probably via a short-lived γ-Fe 2 O 3 (maghemite) phase.(doi: 10.5562/cca1943)